A number of technologies have been investigated in the search to develop an economical method for desalinating water to satisfy the demand for fresh water.
For example, U.S. Pat. No. 6,695,951 to Bitterly et al discloses a series of rotating thin concentric shells which rotate at high velocity. Contaminated liquid is injected onto the surface of the shells. Centrifugal force causes the liquid to form a thin film along the inward-facing surface of the shell. A compressor lowers the pressure adjacent the thin film causing the liquid to boil. The compressor carries the vapor to the other side of the shells at a slightly higher temperature. There the vapor encounters the wall which is cooler because the heat was transferred to boil the contaminated liquid the vapor condenses and rotation throws the condensate against the adjacent wall where it is collected. Heat of condensation is transferred to the shell for boiling contaminated liquid.
This disclosure is characterized by a requirement for large kinetic energy of rotation that is necessary to sustain the process.
U.S. Pat. No. 6,699,369 discloses an apparatus that atomizes seawater using non-pneumatic nozzles. The seawater spray stream is directed into an evaporation chamber air, heated by waste heat is directed. The resultant micro-droplets undergo rapid evaporation resulting in the separation of salt solids from the vapor phase of the water. The mixture of suspended solids and water is filtered to remove and collect the salts. Water vapor is condensed to collect salt free water.
This system is characterized by a requirement to dissipate unused energy of condensation.
U.S. Pat. No. 6,833,056 discloses an apparatus including a heat exchanger cooperating with an evaporation can so as to subject raw water in the evaporation can to heat exchange and thereby generate water vapor in the evaporation can. A condenser cooperates with a raw water tank to receive water vapor from an evaporator can. Subjecting water vapor cools the water vapor and raw water in the raw water tank to heat exchange and thereby obtain distilled water.
In other widely used processes, reverse osmosis has gained the majority market share because of its superior cost performance.
Water produced by reverse osmosis remains an expensive process compared to natural water so the search goes on to satisfy an ever-growing demand. Several types of reverse osmosis have been disclosed and are on the market. The popular commercial systems of choice (as judged in terms of market share) uses TEFLON™ as the membrane material for the reverse osmosis process. The membranes are manufactured by U.S.FILTERS, Inc.
The reverse osmosis systems are expensive to maintain and require up to 800 pounds per square inch to operate. These membranes last only a period of about seven years.
Furthermore, the toxic bacteria that builds up cannot be conveniently cleaned from the TEFLON membrane because the Teflon is degraded by cleansing compounds containing chlorine.